The recently developed PCR-technique has led to great advances in a number of important diagnostic sectors, e.g. the diagnosis of many different diseases, determinations of paternity, forensic medicine, etc. When it is desired to detect RNA, a necessary preliminary stage is the conversion of the RNA into DNA by means of the enzyme reverse transcriptase. The diagnosis of AIDS is routinely made by the detection of antibodies to the HIV-virus in the blood by means of an ELISA (Enzyme Linked ImmunoSorbent)-test. A person may, however, be HIV-positive without antibodies being present if he/she, for instance, is in the early stages of the disease. In this case the ELISA test gives a negative result and the person concerned then risks unwittingly transmitting the infection to others. Therefore the need for a better, i.e. more sensitive, HIV test is very great. The diagnosis of other viruses, also, the culture of which previously took a long time, has been improved with the PCR technique.
As regards the practical procedure, PCR diagnosis comprises three stages:
1) preparation of the reaction mixtures, i.e. preparation of the samples to be tested;
2) the actual amplification, i.e. the chain reaction in which the DNA molecules are replicated exponentially; and
3) the detection of positive samples by means of electrophoresis or hybridisation.
A disadvantage of the PCR method which the present inventor aims to eliminate is that stage 1) is time-consuming and demanding work, primarily because the reagents cannot be mixed in advance, and thus gives rise to many sources of error. It is very important that stage 1) should be carried out with great care and precision because the amplification in stage 2) and the detection result in stage 3) depend absolutely on the reliability of stage 1).
During the various stages of preparing the reagents for a biochemical reaction, such as PCR mentioned above, there is a risk of cross-contamination between the different reaction vessels or test tubes.
While preparing for a PCR reaction there is also a risk of so-called "carry-over contamination" from the person who handles the sample. This applies especially to routine analysis to detect a specific DNA if the same person carries out all the stages before PCR reaction and also handles the PCR product. On skin, hair and laboratory clothing there may be remnants of PCR products from amplifications carried out previously which engender "false" positive results. The risk of false positive results increases the more sensitive the test. The test for HIV is very sensitive and it need scarcely be said that a false positive result causes needless distress to the individual notified of it.